flickr is the exception, because it's all about the pictures.
social networking as a thing unto itself is vastly overrated, by the same set of emerging technocrats who always think the tool is the thing that matters, not the changes the tool makes manifest. it's terrific that we've found a set of conventions that allow us to take advantage of, and actively enhance, the minutiae of human connection. but at the same time, it's just a design thing, a pattern expressed, in the same way that the cart made online shopping and tabs gave us a common frame for navigation. the network is the plumbing, and long-term, about as interesting (which is to say, very, but in the background, and for other reasons.)